1. Field of the Invention
The present invention relates to a fluid-operated cylinder adapted for use as a load lifting cylinder for industrial load handling machines, such as a lift truck and an automated guided vehicle. More particularly, the present invention relates to a fluid-operated cylinder provided with a flow rate control valve operable to cushion a shock occurring when the piston of the fluid-operated cylinder starts from and stops at the ends of a piston stroke.
2. Description of the Related Art
It is well known that in the conventional fluid-operated lift cylinder used, for example, for industrial lift trucks, a shock occurs when the piston begins to move from and stops at the ends of the piston stroke. To eliminate this defect, there has already been proposed a shock cushioning mechanism incorporated in the lift cylinder. However, when the operation of this conventional shock cushioning mechanism (explained later in detail with reference to the drawings) is considered, it is obvious that the mechanism cannot decelerate the movement of the piston through the final stage of the downward piston stroke. That is, the piston has a constant speed even when it comes to the downward end of piston stroke. Therefore, the shock cushioning mechanism cannot completely cushion a shock which occurs when the piston reaches the bottom of the cylinder casing 20. Further, this conventional shock cushioning mechanism cannot absorb a shock which occurs when the piston is moved upward from the bottom of the cylinder casing. This is because the fixed and movable throttle valves of this prior art mechanism cannot control the speed of the upward movement of the piston and piston rod. Also, the conventional fluid-operated cylinder is not provided with a means for cushioning a shock occurring when the piston reaches the upper end of the piston stroke and starts to move down to begin the downward piston stroke.